textproduct: Quad Cities

KEY MESSAGES

- Widespread rainfall is expected early Sunday morning through Sunday evening (70-100% rain chances). Accumulations of 1-3 inches are likely along and south of Highway 34, with a Moderate Risk (level 3 of 4) for excessive rainfall remaining across portions of northeast Missouri into west-central Illinois.

- A Marginal Risk (level 1 of 5) for severe weather remains for Sunday, mainly south of Highway 34. Primary threat is damaging winds, with a lower chance of a tornado.

- Weak disturbances and northwesterly flow aloft to keep temperatures comfortable and slightly below average through the end of next week.

SHORT TERM /THROUGH SUNDAY NIGHT/

Issued at 157 PM CDT Sat Jun 20 2026

Most of tonight should remain quiet as the last bits of surface high pressure shift off to the east, giving way to a rainy system to impact the area on Sunday. Light and variable winds are expected under the high pressure, with low temperatures dipping to the middle to upper 50s for most locations.

Okay, let's talk the Sunday system. A mid-level shortwave trough, currently seen over the Rockies per latest GOES-East mid-level water vapor imagery, will continue to translate eastward with time tonight into Sunday. An attendant area of low pressure will develop via lee cyclogenesis, and both the GEFS and ECMWF ensembles suggest the low track will be along the Iowa/Missouri border. A potent 35 to 45 knot LLJ will support enhanced moisture transport towards our region. The signal among all of the various ensemble guidance continues to show this system packing anomalously high moisture, with the 20.12z HREF ensemble Pwat values around 1.5 up to 2 inches - highest across our southern tier or two of counties closer to the LLJ and higher integrated water vapor transport. These values would be in excess of the 98th percentile per the ECMWF precipitable water climatological percentiles, so anomalously high even for this time of the year. As far as QPF is concerned, one thing that was noticed is that a dProg/dt of the latest HREF ensemble probability-matched mean QPF shows a northern shift in the axis of the heaviest QPF, likely owing to a more poleward shift in the nose of the LLJ. The 6-hour PMM QPF per the HREF between 12z-18z Sunday is now around 2-3+", centered on the Highway 34 corridor and points south, which has led to continued concern for flash flooding potential given that the latest flash flood guidance values are now around 2 inches in these areas. Due to this northern shift, we decided to expand the Flood Watch northward to the Highway 34 corridor (now valid through 00z Monday/7 PM Sunday). If the northern trend in higher QPF continues, it's possible we will need to expand the Flood Watch even further. The latest excessive rainfall outlook from WPC indicates little change, with a Moderate Risk (level 3 of 4) for our southern tier of counties, and a Slight risk (level 2 of 4) for areas south of Highway 30.

As for the severe weather potential, there hasn't been much change in that as SPC continues to maintain a Marginal Risk (level 1 of 5) for our southern tier of counties. While the morning will bring the bulk of the rainfall for this event, the afternoon could be our period to watch for any isolated strong/severe storms as the actual surface low translates across our south at that time. There are questions on how much destabilization will occur due to the resulting rain-cooled air. At the moment, damaging winds appear to be the primary threat with any severe storms, given deep-layer shear values around 35 to 45 knots and modest instability, with SBCAPE values around 500-1000 J/kg per the HREF ensemble. One thing to watch for is the (lower) potential for tornadoes as low-level shear looks actually pretty decent (100 to 200 m2/s2 of 0-1 km SRH). However, storms will need to become surface-based in order to tap into this kind of available streamwise vorticity, so this appears to be a more unlikely threat. Even if severe weather doesn't materialize, a tight surface pressure gradient should still support some gusty east-northeast winds, with gusts likely around 20 to 30 mph.

Eventually, the surface low pressure system will exit the region to the east, bringing the bulk of the showers and thunderstorms to an end. There could be some lingering light showers in the evening as the mid-level shortwave lags behind the surface low, but confidence in this is fairly low (20-40% chances). Otherwise, Sunday night looks to be largely dry, with lows falling to the lower to middle 50s.

LONG TERM /MONDAY THROUGH FRIDAY/

Issued at 157 PM CDT Sat Jun 20 2026

Monday-Tuesday...Behind the Sunday shortwave, zonal flow returns aloft, keeping conditions dry on Monday. Northerly winds at the surface will keep highs in the 70s and lows in the 50s Monday into Tuesday morning underneath partly cloudy skies. On Tuesday, the next shortwave trough digs southward into the Northern Plains. Another low pressure develops ahead of this trough across the Dakotas, but the positive tilt of the trough does not provide a lot of upper level support for deepening. This low pressure will swing southeastward with the trough, bringing PoPs back up Tuesday night along the cold front. The orientation of this system should limit the severe potential.

Wednesday-Friday...As the low pressure from Tuesday night clears the area, a weak surface trough develops on the backside, keeping some light showers around as the positively-tilted upper-level trough moves over Iowa. PoPs should drop off heading into Wednesday night as convergence aloft on the backside of the trough allows for subsidence to set in. Weak perturbations in the northwesterly flow aloft will keep diurnal-driven scattered PoPs on the table Friday. In addition, weak northerly flow at the surface during this time period should keep highs in the 70s (70-90% chance), below average for this time of year.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 1236 PM CDT Sat Jun 20 2026

VFR conditions will continue into tonight, with only some FEW to SCT daytime cumulus clouds and persistent northwest winds around 5-15 knots becoming light and variable overnight. Attention will then turn to a rainy system that will begin moving in from the west around dawn Sunday, bringing bouts of heavy rainfall with it (70-100% chance). As a result, MVFR to IFR ceilings and visibilities are expected with this activity. The onset timing of rain remains uncertainty, but decided to forecast prevailing SHRA when confidence in rainfall was high enough. There could also be some embedded thunderstorms near BRL, with much lower confidence in storms farther north.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Flood Watch from Sunday morning through Sunday evening for IAZ087>089-098. Flood Watch from Sunday morning through Sunday evening for IAZ099. IL...Flood Watch from Sunday morning through Sunday evening for ILZ025-026. Flood Watch from Sunday morning through Sunday evening for ILZ034-035. MO...Flood Watch from Sunday morning through Sunday evening for MOZ009-010.